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Re: [Qemu-devel] [RFC/RFT PATCH 0/7] cpu-exec: simplify cpu_exec and rem
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [RFC/RFT PATCH 0/7] cpu-exec: simplify cpu_exec and remove some icount special cases |
Date: |
Wed, 15 Feb 2017 13:42:21 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0 |
On 29/01/2017 22:09, Paolo Bonzini wrote:
> The series includes three parts:
>
> 1-2: fix two bugs, the first one pretty bad, the second seems
> to be theoretical only.
>
> 3-5: simplify cpu_exec. This builds on Sergey's conversion
> of cpu_exec to a simple top-down logic, making the phases
> clearer and saving on the cost of siglongjmp in the meanwhile.
I'll include these five in my next pull request. Review for patch 6 is
welcome!
Paolo
> 6-7: these are intended to be a base for Pavel's record/replay
> fixes. The main thing I noticed while reviewing is that icount
> is redoing (with u16.high) a lot of things that tcg_exit_req is
> doing too. This is because, at the time icount was introduced,
> tcg_exit_req didn't exist and QEMU instead unwound chained TBs
> through POSIX signals. But now we have essentially two ways to
> do the same thing with subtly different invariants or downright
> bugs (such as the one fixed by patch 1). Patch 6 therefore
> unifies tcg_exit_req and the icount interrupt flag. It saves a
> handful of instructions per TB in icount mode and generally
> makes icount mode "less special", which is a good thing since
> no one seems to understand it well. Patch 7 then removes another
> EXCP_INTERRUPT/cpu_loop_exit pair; by exiting to main loop simply
> through cpu->exit_request, hopefully it fixes one of the issues that
> Pavel was seeing.
>
> For now I've tested this only on an aarch64 Linux image (with
> and without -icount). Thanks,
>
> Paolo
>
> Paolo Bonzini (7):
> cpu-exec: fix jmp_first out-of-bounds access with icount
> cpu-exec: tighten barrier on TCG_EXIT_REQUESTED
> cpu-exec: avoid cpu_loop_exit in cpu_handle_interrupt
> cpu-exec: avoid repeated sigsetjmp on interrupts
> cpu-exec: remove outermost infinite loop
> cpu-exec: unify icount_decr and tcg_exit_req
> cpu-exec: centralize exiting to the main loop
>
> cpu-exec.c | 153
> +++++++++++++++++++++-------------------------
> include/exec/exec-all.h | 1 +
> include/exec/gen-icount.h | 53 ++++++++--------
> include/qom/cpu.h | 15 +++--
> qom/cpu.c | 2 +-
> tcg/tcg.h | 1 -
> translate-all.c | 2 +-
> translate-common.c | 13 ++--
> 8 files changed, 109 insertions(+), 131 deletions(-)
>